An embodiment relates to time of flight estimation.
Passive entry/passive start systems allow a user to passively enable entry to a vehicle or enable vehicle operations without having to directly utilize a key or manually actuate a fob for entering/starting a vehicle. Such passive systems operate by monitoring a proximity of a use carrying a passive device, such as a passive fob, on oneself, and when a trigger occurs such as touching of a door handle, the system will transmit an interrogation signal from which the fob transmits a reply signal. If the they vehicle and the fob carried by the user are successfully paired, then the doors will unlock without the user having to press an unlock key.
Some passive systems operate based on a wakeup trigger, such that the vehicle system wakes up when an action occurs such as touching the door handle. Others systems could continuously transmit an interrogation signal and monitor for a fob in the proximity without a wake up action; however, a continuous transmission of an interrogation signal could cause battery drain or other issues. That is, if the interrogation signal is transmitted at a low rate (long intermission period between interrogation signal transmissions such as 10 second), then a user's action of attempting to open the door may not be detected if the user approaches in between the transmitted interrogation signals which would be a nuisance if door remains locked while the user attempts to open the door. This could also cause warranty issues as the user may conclude that the system is not operating properly. Alternatively, if the system sends out interrogations signals at a high rate (small intermission period between interrogation signal transmissions such as 1 millisecond), then battery drain could occur due to excessive energy consumption.